Fuel Production from the Electroreduction of CO2

Introduction

Electrochemical reduction is a highly effective method for converting CO₂ to CO, organic acids, low molecular weight hydrocarbons and alcohols.  Product distribution from the reduction of CO₂ is highly dependent on the composition and preparation of the catalysts and reduction potential, as such, multiple reduction pathways are observed depending on the catalysts material and the preparation methods.

Copper and its alloys have been found to produce higher molecular weight hydrocarbons, such as ethylene, methanol and ethanol.  Here we demonstrate a high surface area Cu alloy catalysts that has a preferential selectivity towards the formation of C2 and C3 species.  This paper will also discuss our attempts to understand the mechanistic pathway using in-situ vibrational spectroscopy under reaction conditions.

Experimental

A copper/aluminum alloy was used as the starting material for producing a high surface area copper catalyst.  The aluminum was removed through an etching procedure in strong base. The resulting nanoporous copper was crushed and mixed with Nafion, a binding agent, then casted over a copper foil substrate.  Carbon dioxide electroreduction was performed by placing the catalyst in a specially designed flow cell. A bubbler in the cell was used to deliver CO₂ to saturate the electrolyte, 0.1 M KHCO₃, at a rate of 10 mL/min. The catalyst acts as the working electrode in this electrochemical cell. The product distribution from the electroreduction process was collected at a series of potentials. Gaseous products were identified and quantified using gas chromatography coupled with both mass spectrometry and a thermal conductivity detector.  Liquid products were analyzed using nuclear magnetic resonance.

The surface morphology and composition of the catalyst was characterized using scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS).  The SEM images show a rough surface that retains a porous structure before and after experiments. XPS studies incorporated depth profiling, and show that ruthenium from the surface of the material migrates to the bulk after electrolysis.